Transparent thermoplastic polymer blend compositions for use in molded and extruded articles are disclosed herein.
A variety of transparent thermoplastic compositions have been developed, some of which have been disclosed in the patent literature and/or introduced to the marketplace. Each of those compositions has a particular level of transparency, often characterized in terms of “haze,” which is expressed as (%) in accordance with recognized test procedures. Shortcomings of those compositions include unsatisfactorily high haze values (low transparency), poor processability and poor mechanical properties, including undue hardness, low flexibility, etc. For example, previously proposed thermoplastic elastomer compositions with transparency and flexibility such as compounds based on styrene-ethylene-butadiene-styrene block copolymers, thermoplastic vulcanizate blends (TPV) or thermoplastic olefin (TPO) blends have reached transparency and softness levels that are still unsatisfactory in some applications.
It is among the objects of the invention to provide a transparent material that has a desirable balance of softness, flexibility and strength, and which can be easily processed in a molten state in extrusion or molding.
Polymer blends prepared for various applications are known. Adhesive blends that include hydrocarbon resins are disclosed in WO 04/087806. In Example 4 certain compositions include hydrocarbon resin with Tg>20° C. blended with two different types of polypropylenes, namely, minor amounts of polypropylene having a Tm≧110° C. and major amounts (72 wt % and above) of propylene-ethylene copolymer that has isotactically arranged propylene derived sequences and Tm<105° C.
U.S. Pat. No. 5,317,070 also discloses adhesive compositions that include a hydrocarbon resin with high glass transition temperature, but the polymers with which the compositions are blended are different from the polypropylenes claimed herein. U.S. Pat. No. 6,500,563 discloses blends of two different types of polypropylene, including blends made from a polypropylene having a Tm≧110° C. and propylene-ethylene copolymer that has isotactically-arranged propylene-derived sequences and Tm<105° C.
Three component blends of isotactic polypropylene, impact modifying amounts of an ethylene propylene based rubber or low density ethylene copolymer and a propylene-based elastomer as compatibilizer are described in EP946640, EP964641, EP969043 and EP1098934.
WO 04/014988 describes blends of isotactic polypropylene with non-functionalized plasticizers such as poly-alpha-olefins. WO 04/060994 describes blends of polypropylene and propylene-based elastomers to provide flexibility. WO03/040233 discloses two component blends with the isotactic polypropylene as the predominant, matrix phase and the propylene-based copolymer serving as an impact modifier. EP1003814 and U.S. Pat. No. 6,642,316 disclose two-component blends of small amounts of isotactic polypropylene and predominant amounts of an ethylene-based elastomer. EP374695 Example 5 discloses visually homogeneous two component blends however using 40 wt % or less of the propylene-based copolymer. WO00/69963 describes films made of two—component blends with from 75 to 98 wt % of a propylene ethylene based elastomer having a heat of fusion of less than 25 J/g. A process oil may be present.
Others have attempted to make transparent compositions, but many of such compositions are problematic, particularly when attempting to make molded compositions that possess a desirable array of properties, such as softness, flexibility and strength, while also having good processability. For example, others have been confronted with shortcomings in the area of processability, particularly for molded or extruded compositions, where the tendency for a material to crystallize quickly has enormous advantages. Many materials that have good mechanical properties lack good crystallization properties. When a composition is used for molding, it is desirable that it have a tendency to flow well and thus quickly and easily and completely fill all areas of the mold. While there is a general tendency for higher MFR materials to correspond to good flowability, a higher MFR is frequently also accompanied by an unfortunate decrease in mechanical properties; thus a higher MFR is not necessarily desirable for that reason. Furthermore, many compositions experience a trade-off in properties, e.g., where good mechanical properties may be offset by poor flexibility, e.g., undue stiffness or hardness. Accordingly, there is a need for a material that has a combination of desirable properties.
The compositions of the present invention combine the ease of fabrication by molding processes such as thermoforming, blow molding or injection molding or extrusion processes with transparency and elasticity. These primary properties are combined with the ability to vary the tensile strength and the hardness by the changes in the composition particularly in the balance of the FPC and the SPC as well as the MFR of the SPC. There is a need in the art for such elastic and transparent polyolefin compositions which can be easily fabricated.